In a substrate processing apparatus such as a plasma processing apparatus used to manufacture semiconductor devices, product wafers in a substrate storage container are taken out of the substrate storage container and carried into a processing chamber one at a time. The product wafer placed in the processing chamber then undergoes processing such as etching or film formation with plasma raised from a processing gas supplied into the processing chamber.
In the substrate processing apparatus, it is crucial to eliminate in an optimal manner particles (fine particles of foreign matter) of reaction products formed as the product wafer is processed inside the processing chamber or particulates entering the processing chamber from the outside.
For instance, particles remaining on the substrate stage disposed inside the processing chamber may adhere to the rear surface of the product wafer placed on the stage and this may adversely affect the subsequent processes to a significant extent. In addition, particles remaining inside the processing chamber may settle onto the product wafer and affect the processing of the product wafer, which would compromise the quality of the semiconductor devices formed from the product wafer as final products.
In the related art, a dummy wafer is transferred into the processing chamber after a specific number of product wafers have been processed in the processing chamber so as to clean the interior of the processing chamber with specific timing and thus eliminate the particles inside the processing chamber in an effective manner (see, for instance, Japanese Laid Open Patent Publication No. 2007-250791).
The substrate processing apparatus may be equipped with an interrupt processing function whereby an interrupt wafer, different from product wafers, is processed with priority by cutting into the processing of product wafers. At such a substrate processing apparatus, with a separate substrate storage container holding interrupt wafers disposed therein, an interrupt wafer taken out of the substrate storage container is transferred into the processing chamber and processing on the interrupt wafer starts in response to an interrupt start operation executed with desired timing, even if the processing of the current lot of product wafers is in progress.
However, since the timing with which the interrupt wafer is transferred is not specially regulated in the related art, the interrupt wafer is taken out of the substrate storage container immediately in response to the interrupt start operation. This gives rise to an undesirable situation that may occur in the substrate processing apparatus that executes the cleaning process with specific timing following the processing executed on the specific number of product wafers, as described earlier, in that depending upon the timing of the interrupt start operation, the interrupt wafer may be transferred in succession with respect to a product wafer.
In other words, when a dummy wafer to be used in the cleaning process is to be carried into the processing chamber next, the interrupt wafer transferred immediately after the product wafer cuts into the flow and the manufacturing process is continuously executed (on the product wafer and the interrupt wafer). In this situation, the cleaning process will be executed on the dummy wafer transferred into the processing chamber after the interrupt wafer. As a result, the timing with which the cleaning process is executed inside the processing chamber will be disrupted which, in turn, will destabilize the conditions inside the processing chamber and ultimately cause inconsistency in the results of the manufacturing process executed on the individual wafers.
An object of the present invention, having been completed by addressing the issues discussed above, is to provide a substrate processing apparatus that does not allow the interrupt substrate processing to destabilize conditions inside the processing chamber and a substrate transfer method that may be adopted in the substrate processing apparatus.